A method for removing aluminum from brine used in chlor-alkali electrolysis process

Abstract

The invention provides a method for removing aluminum elements in brine used in a chlor-alkali electrolysis process, comprising: S1, mixing water with raw salt to obtain saturated crude brine; S2, sending the saturated crude brine, sodium carbonate and sodium hydroxide into a primary reaction tank to react and generate calcium carbonate and magnesium hydroxide; S3, sending disodium hydrogen phosphate and a mixed solution in the primary reaction tank into a secondary reaction tank, and the remaining calcium and magnesium ions react to generate calcium hydrogen phosphate and magnesium hydrogen phosphate; S4, sending the mixed solution in the secondary reaction tank into a filter for filtration; S5, adding hydrochloric acid to the filtered brine, sending the brine into a buffer tank, so that the pH of the brine in the buffer tank is 5-6, and the aluminum element reacts to generate aluminum hydroxide colloid; S6, sending the mixed solution in the buffer tank into a filtering device for filtration, and sending the filtered clear liquid into a brine tank. The invention can effectively reduce the calcium / magnesium ion content and the aluminum element content in the brine, is beneficial to reducing the adsorption load of a resin tower, and improves the quality of the raw material liquid sent to an ion membrane electrolyzer.

Description

Technical Field

[0001] The invention relates to a method for removing aluminum element from brine used in chlor-alkali electrolysis process. Background Art

[0002] In the chlor-alkali ion membrane electrolysis process, the metal ion content in the brine has a great influence on the efficient operation of the ion membrane. Before the brine is fed into the electrolytic cell, it is often necessary to remove the Ca 2+ / Mg 2+ The control index is below 20PPb, and the control index of aluminum is below 100PPb. 2+ / Mg 2+ Chemical precipitation combined with resin adsorption can be used to achieve the standard, but the aluminum element in the brine is different from calcium and magnesium. Since aluminum has both acidic and alkaline properties, it has a high solubility in both acidic and alkaline environments. This means that the existing technology often cannot directly add refining agents to form water-insoluble substances to remove the aluminum element, and it is also difficult to reduce the aluminum content through resin adsorption. Therefore, there is currently no effective aluminum removal production process in the chlor-alkali industry, and the high aluminum content in the brine entering the tank has gradually become a production bottleneck restricting the chlor-alkali industry.

[0003] Therefore, in the prior art for treating crude brine, after removing calcium and magnesium, it is often difficult to effectively remove aluminum, resulting in a relatively high aluminum content in the brine. Summary of the invention

[0004] In view of this, the present invention aims to propose a method for removing aluminum from brine used in a chlor-alkali electrolysis process, so as to solve the problem that the prior art is difficult to effectively remove aluminum, resulting in a relatively high aluminum content in the brine.

[0005] To achieve the above object, the technical solution of the present invention is achieved as follows:

[0006] A method for removing aluminum elements from brine used in a chlor-alkali electrolysis process comprises: S1, mixing water with solid raw salt to obtain saturated crude brine; S2, sending the saturated crude brine, sodium carbonate and sodium hydroxide into a primary reaction tank to fully react to generate calcium carbonate and magnesium hydroxide; S3, sending disodium hydrogen phosphate and a mixed solution in the primary reaction tank into a secondary reaction tank to fully react with the remaining calcium and magnesium ions to generate calcium hydrogen phosphate and magnesium hydrogen phosphate; S4, sending the mixed solution in the secondary reaction tank into a filter for filtration; S5, adding hydrochloric acid to the filtered brine and sending it into a buffer tank to make the pH of the brine in the buffer tank be 5-6, and the aluminum element reacts to generate aluminum hydroxide colloid; S6, sending the mixed solution in the buffer tank into a filtering device for filtration, and sending the filtered clear liquid into a brine tank.

[0007] Furthermore, the water in step S1 at least includes dechlorinated salt water containing hypochlorite ions returned from the downstream ion membrane electrolysis process.

[0008] Furthermore, the hypochlorite ion concentration in the dechlorinated brine is 5-40 mg / L, and the chlorate ion concentration in the mixed solution at the outlet of the secondary reaction tank is lower than 1-3 mg / L, so that the organic matter content in the mixed solution at the outlet of the secondary reaction tank is ≤10 ppm.

[0009] Furthermore, in step S2, based on the unit volume of saturated crude brine, the amount of sodium carbonate over-alkali is 300-500 mg / L, and the amount of sodium hydroxide over-alkali is 100-300 mg / L; the temperature of the mixed liquid in the primary reaction tank is not less than 55°C.

[0010] Furthermore, in step S3, based on the residual calcium and magnesium ion contents in the mixed solution fed into the secondary reaction tank, the amount of disodium hydrogen phosphate added exceeds the theoretical amount required for the reaction by 10-20 ppm; and the temperature of the mixed solution in the secondary reaction tank is 10-20°C.

[0011] Further, in step S5, the buffer tank includes a tank body, the tank body has a discharge port and a liquid inlet, the brine pipe is connected to the liquid inlet of the tank body, and a Venturi acidifier and a pH meter are sequentially arranged in the brine pipe along the direction of brine flow, the Venturi acidifier has an acid addition port, and the acid addition port is connected to the hydrochloric acid main line, a main regulating valve is arranged in the hydrochloric acid main line, the hydrochloric acid main line has a branch pipe connected in parallel with the main regulating valve, and a fine-tuning valve is arranged in the branch pipe.

[0012] Furthermore, a compressed air pipe and a gas distributor are arranged in the tank body, one end of the compressed air pipe is connected to an external air source, and the other end is connected to the gas distributor, and the gas distributor has a plurality of evenly distributed air outlet holes.

[0013] Furthermore, in step S6, the filtering device is a cross-flow filtering device.

[0014] Furthermore, the cross-flow filtration device includes a shell, an outer core and an inner core are arranged inside the shell, the inner core is arranged inside the outer core, and the inner core and the outer core are arranged coaxially, the inner core has a first filter cavity inside, a brine cavity is formed between the inner core and the outer core, a second filter cavity is formed between the shell and the outer core, and the inner core and the outer core can at least rotate in opposite directions relative to each other.

[0015] Furthermore, the cross-flow filtration device includes a driving device, a central axis is arranged at the bottom of the inner core, an outer shaft sleeve is arranged at the bottom of the outer core, the outer shaft sleeve is sleeved on the outside of the central axis and is arranged coaxially with the central axis, the central axis and the outer shaft sleeve can rotate relative to each other, and the central axis and the outer shaft sleeve are respectively connected to the driving device, so that the inner core and the outer core can at least rotate in opposite directions to each other.

[0016] Compared with the prior art, the method for removing aluminum from brine used in chlor-alkali electrolysis process described in the present invention has the following advantages:

[0017] The method for removing aluminum elements from salt water used in a chlor-alkali electrolysis process of the present invention first utilizes the dechlorinated light salt water returned from the downstream ion membrane electrolysis process and utilizes the hypochlorite ions therein to efficiently remove natural organic matter such as bacteria, algae, humic acid, etc. in the salt water at the stage of preparing saturated crude salt water by salt treatment. Not only does it not require the additional addition of sodium hypochlorite, it reduces the additional agent delivery and eliminates the corresponding agent delivery equipment. Moreover, it can effectively reduce the organic matter content on the basis of minimizing the residual hypochlorite ions, avoid interference with the calcium, magnesium, and aluminum element removal process, avoid the organic matter carried in the water from affecting the normal working environment of the chelating resin tower, and improve the quality of the raw material liquid sent to the subsequent ion membrane electrolyzer.

[0018] At the same time, the present application utilizes a relatively high temperature primary reaction tank to perform a first-stage reaction to remove calcium / magnesium ions, and then utilizes a relatively low temperature secondary reaction tank to perform a second-stage reaction to remove calcium / magnesium ions remaining in the brine, thereby realizing two-stage removal of calcium / magnesium ions, and after filtering the calcium / magnesium precipitate, by adjusting the pH of the brine, the aluminum element forms as much aluminum hydroxide colloid as possible, and utilizes a cross-flow filtration device to remove the aluminum hydroxide; thereby, the calcium / magnesium ion content and the aluminum element content in the brine can be effectively reduced, and the removal effect of calcium / magnesium ions and aluminum elements can be fully improved, which is beneficial to reducing the adsorption load of the chelating resin tower, improving the quality of the raw liquid sent to the subsequent ion membrane electrolyzer, and is beneficial to extending the regeneration cycle or service life of downstream equipment such as the resin tower and the ion membrane electrolyzer. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] The accompanying drawings constituting a part of the present invention are used to provide a further understanding of the present invention. The exemplary embodiments of the present invention and their descriptions are used to explain the present invention and do not constitute an improper limitation of the present invention. In the accompanying drawings:

[0020] Figure 1 A process block diagram of a method for removing aluminum from brine used in a chlor-alkali electrolysis process according to an embodiment of the present invention;

[0021] Figure 2 This is a schematic diagram of the structure of a buffer tank according to an embodiment of the present invention;

[0022] Figure 3 It is a schematic structural diagram of a cross-flow filtration device according to an embodiment of the present invention;

[0023] Figure 4 It is a simplified structural diagram of a driving device in a cross-flow filtering device according to an embodiment of the present invention;

[0024] Figure 5 It is a schematic diagram of the structure of the gear assembly in the driving device according to an embodiment of the present invention.

[0025] Description of reference numerals:

[0026] 1. Shell; 2. Inner core; 21. Central axis; 3. Outer core; 31. Outer sleeve; 4. Driving device; 5. Brine chamber; 6. First filter chamber; 61. Liquid extraction tube; 7. Second filter chamber; 71. Liquid outlet; 81. Central gear; 82. Planetary gear; 83. Driven gear ring; 84. Planetary carrier; 85. Box; 91. Rotor; 92. Stator; 101. Tank; 102. Brine pipe; 103. Venturi acidifier; 104. pH meter; 105. Hydrochloric acid main line; 106. Branch pipe; 107. Compressed air pipe; 108. Gas distributor; 109. Liquid outlet. DETAILED DESCRIPTION

[0027] The inventive concepts of the present disclosure will be described below using terms commonly used by those skilled in the art to convey the essence of their work to other persons skilled in the art. However, these inventive concepts can be embodied in many different forms and should not be considered limited to the embodiments described herein.

[0028] It should be noted that, in the absence of conflict, the embodiments of the present invention and the features in the embodiments may be combined with each other.

[0029] The present invention will be described in detail below with reference to the accompanying drawings and in conjunction with embodiments.

[0030] In order to solve the problem that the existing technology is difficult to effectively remove aluminum, resulting in a relatively high aluminum content in brine, this embodiment proposes a method for removing aluminum from brine used in a chlor-alkali electrolysis process, as shown in the attached Figure 1 As shown, the method includes:

[0031] S1, mixing water and solid raw salt to obtain saturated crude brine;

[0032] The water in step S1 at least includes dechlorinated brine containing hypochlorite ions returned from the downstream ion membrane electrolysis process, so that in the process of preparing saturated crude brine by salt treatment, there is no need to add additional sodium hypochlorite, which reduces the amount of additional reagents and can also achieve efficient removal of natural organic matter such as bacteria, algae, humic acid, etc. in the brine.

[0033] Specifically, the concentration of hypochlorite ions in the dechlorinated light salt water is 5-40 mg / L (with the dechlorinated light salt water as a reference), and the concentration of chlorate ions in the mixed solution at the outlet of the secondary reaction tank should be ensured to be lower than 1-3 mg / L (with the mixed solution at the outlet of the secondary reaction tank as a reference), preferably lower than 1 mg / L. Accordingly, the natural organic matter such as algae, humic acid, etc. in the salt water is removed by relatively slightly excessive hypochlorite ions, so that the organic matter content in the mixed solution at the outlet of the secondary reaction tank is ≤10ppm. Thus, without the need to add additional sodium hypochlorite and reduce the dosage of the agent, by further regulating the concentration of hypochlorite ions, the organic matter content can be effectively reduced on the basis of leaving no residual hypochlorite ions as far as possible, which can not only avoid interference with the removal process of calcium, magnesium, and aluminum elements, but also avoid the organic matter carried in the water from affecting the normal working environment of the chelating resin tower, and can also improve the quality of the raw liquid sent to the subsequent ion membrane electrolyzer.

[0034] In addition, the water may include industrial water, filtrate from a plate and frame filter press, miscellaneous water from diaphragm electrolysis, etc., in addition to the dechlorinated brine containing hypochlorite ions returned from the downstream ion membrane electrolysis process. The specific process of step S1 is roughly as follows: water is pumped into a water bucket, and then pumped from the water bucket into a salt tank as a solvent; solid raw salt is unloaded from a salt unloader to a salt field, and then sent to a salt tank by a crane; saturated crude brine is obtained by dissolving the raw salt in the salt tank, and the saturated crude brine in the salt tank overflows into a crude brine receiving bucket, and then is pumped to a brine receiving tank in the factory by a crude brine pump.

[0035] S2, sending saturated crude brine, sodium carbonate and sodium hydroxide into a primary reaction tank to fully react to generate calcium carbonate and magnesium hydroxide;

[0036] Among them, based on the unit volume of saturated crude brine, the amount of sodium carbonate is 300-500 mg / L, and the amount of sodium hydroxide is 100-300 mg / L, so that the amount of sodium carbonate and sodium hydroxide added exceeds the theoretical amount required for the reaction and tries not to exceed the water quality standard required for production. Among them, sodium carbonate and sodium hydroxide can be added to the crude brine in solid form, or they can be prepared in advance into solutions of appropriate concentrations and added to the crude brine, such as: sodium carbonate and sodium hydroxide are prepared into saturated solutions respectively, and added to the crude brine respectively.

[0037] In order to increase the reaction rate in the primary reaction tank, the primary reaction tank is provided with a heating device so that the temperature of the mixed liquid in the primary reaction tank is not less than 55°C; preferably, the heating device is steam heating, and a plurality of steam heating pipes are evenly arranged in the primary reaction tank, and the steam heating pipes have a steam outlet for directly conveying steam into the primary reaction tank. While improving the heating efficiency and the reaction rate, the influx of steam into the mixed brine can also increase the turbulence of the brine, avoid the appearance of static dead zones of different densities in the brine, and allow the materials to fully mix and react, which is beneficial to further improve the removal effect of calcium / magnesium ions.

[0038] S3, sending the mixed solution of disodium hydrogen phosphate and the primary reaction tank into the secondary reaction tank, so that the remaining calcium and magnesium ions fully react to form calcium hydrogen phosphate and magnesium hydrogen phosphate;

[0039] The amount of disodium hydrogen phosphate added is slightly excessive, and based on the residual calcium and magnesium ion content in the mixed solution fed into the secondary reaction tank, the amount of disodium hydrogen phosphate added exceeds the theoretical amount required for the reaction by 10-20ppm. Similarly, disodium hydrogen phosphate can be added in solid form, or it can be added after being prepared in advance into a solution of appropriate concentration.

[0040] The temperature of the mixed solution in the secondary reaction tank is 10-20 ° C, that is, the mixed solution in the secondary reaction tank is room temperature (such as conventional 20 ° C) or slightly lower than room temperature, so that the secondary reaction tank maintains a relatively low temperature reaction environment, and the calcium and magnesium ions remaining in the brine can be further removed in the form of calcium hydrogen phosphate and magnesium hydrogen phosphate precipitation, and the dissolution trend of solids (especially slightly soluble substances) can be suppressed, and the precipitation of some solids due to high temperature is not sufficient, which is conducive to further improving the removal effect of calcium / magnesium ions. Specifically, a baffle groove is set between the primary reaction tank and the secondary reaction tank, and the baffle groove preferably has a sufficient length, so that the mixed solution of the relative height in the primary reaction tank can be cooled by the baffle groove and then flow into the secondary reaction tank to ensure that the temperature of the mixed solution in the secondary reaction tank is near room temperature. In addition, preferably, a cooling coil is set in the secondary reaction tank, and when the temperature of the mixed solution in the secondary reaction tank is high, a low-temperature medium (such as low-temperature carbon dioxide, low-temperature Freon, etc.) can be transported to the cooling coil, and the temperature of the mixed solution in the secondary reaction tank is near or below room temperature through the coil heat exchange.

[0041] S4, sending the mixed liquid in the secondary reaction tank into a filter for filtering;

[0042] The filter is a membrane filter, which uses a polytetrafluoroethylene (PTFE) tubular filter membrane. The pore size of the membrane in the membrane filter is 0.22-0.5 μm. The flow rate of a single membrane filter is about 120 cubic meters per hour. It is a large flux filter that can meet large-scale brine treatment processes. In order to maintain a high filtration capacity and a low filtration pressure, the filter needs to be chemically regenerated with a 15% hydrochloric acid solution after running for a certain period of time.

[0043] S5, adding hydrochloric acid to the filtered brine and sending it to a buffer tank, so that the pH of the brine in the buffer tank is 5-6, and the aluminum element reacts to form aluminum hydroxide colloid;

[0044] Among them, since the pH of the brine after the removal of calcium and magnesium ions is about 10, the aluminum element in the brine is mainly dissolved in the water in the form of aluminate. In the process of adjusting the pH, the aluminate in the brine will react to form water-insoluble aluminum hydroxide as the acid-base environment changes.

[0045] In step S5, a compressed air pipe 107 is provided in the buffer tank, and the brine is fully stirred by passing compressed air into the buffer tank to promote the reaction of aluminum element to generate aluminum hydroxide colloid.

[0046] Specific as attached Figure 2 As shown, the buffer tank includes a tank body 101, the tank body 101 has a discharge port 109 and a liquid inlet, a brine pipe 102 is connected to the liquid inlet of the tank body 101, and along the direction of brine flow, a venturi acidifier 103 and a pH meter 104 are sequentially arranged in the brine pipe 102, the venturi acidifier 103 has an acid addition port, and the acid addition port is connected to a hydrochloric acid main line 105, a main regulating valve is arranged in the hydrochloric acid main line 105, and is used to adjust the amount of hydrochloric acid added; the hydrochloric acid main line 105 has a branch pipe 106 connected in parallel with the main regulating valve, and a fine adjustment valve is arranged in the branch pipe 106, and is used to finely adjust the amount of hydrochloric acid added, so as to improve the accuracy of the hydrochloric acid amount adjustment.

[0047] At the operation site, the technician can manually adjust the main regulating valve and the fine regulating valve according to the display of the pH meter. Of course, in order to improve the automation of the chlor-alkali system, the main regulating valve, the fine regulating valve, and the pH meter 104 are all connected to the automatic control system, and the pH value of the brine obtained in real time by the pH meter is used to adjust the main regulating valve and the fine regulating valve accordingly, so that the pH of the brine entering the buffer tank is 5-6.

[0048] A compressed air pipe 107 and a gas distributor 108 are provided in the tank body 101. One end of the compressed air pipe 107 is connected to an external air source, and the other end is connected to the gas distributor 108. The gas distributor 108 has a plurality of evenly distributed air outlet holes, which can improve the uniformity of compressed air distribution in the tank body 101 to ensure that the compressed air fully stirs the brine.

[0049] S6. Send the mixed liquid in the buffer tank to the filtering device for filtration, and send the filtered clear liquid to the brine tank.

[0050] The brine in the brine tank can be sent to the downstream chlor-alkali process, or it can be reused in the salt-making process of step S1.

[0051] Therefore, the present application firstly utilizes the dechlorinated light brine returned from the downstream ion membrane electrolysis process, and utilizes the hypochlorite ions therein to efficiently remove natural organic matter such as bacteria, algae, humic acid, etc. in the brine at the stage of preparing saturated crude brine by salt treatment. Not only does it not require the additional addition of sodium hypochlorite, it reduces the additional agent dosage and eliminates the corresponding agent dosage equipment, but it can also effectively reduce the organic matter content on the basis of minimizing the residual hypochlorite ions, which can not only avoid interference with the calcium, magnesium and aluminum element removal process, but also avoid the organic matter carried in the water from affecting the normal working environment of the chelating resin tower, and can also improve the quality of the raw liquid sent to the subsequent ion membrane electrolyzer.

[0052] At the same time, the present application utilizes a relatively high temperature primary reaction tank to perform a first-stage reaction to remove calcium / magnesium ions, and then utilizes a relatively low temperature secondary reaction tank to perform a second-stage reaction to remove calcium / magnesium ions remaining in the brine, thereby realizing two-stage removal of calcium / magnesium ions, and after filtering the calcium / magnesium precipitate, by adjusting the pH of the brine, the aluminum element forms as much aluminum hydroxide colloid as possible, and utilizes a cross-flow filtration device to remove the aluminum hydroxide; thereby, the calcium / magnesium ion content and the aluminum element content in the brine can be effectively reduced, and the removal effect of calcium / magnesium ions and aluminum elements can be fully improved, which is beneficial to reducing the adsorption load of the chelating resin tower, improving the quality of the raw liquid sent to the subsequent ion membrane electrolyzer, and is beneficial to extending the regeneration cycle or service life of downstream equipment such as the resin tower and the ion membrane electrolyzer.

[0053] In this application, after sampling and testing the corresponding salt water, each material can be added quantitatively by manual or automatic dosing device. Taking automatic dosing as an example, the concentration signal of the specific component in the salt water detected can be converted into an electrical signal and input into the automatic control system through the online detector. Through the control of the automatic control system, the dosing pump can adjust the flow rate and addition amount of the agent in real time. In view of the fact that the technologies such as quantitative dosing and automatic dosing can refer to the existing technology or analytical chemistry technology, this application will not elaborate on them.

[0054] Since the aluminum hydroxide generated by the reaction of aluminum elements is in colloidal form, it is easy to adhere to the surface of the filter membrane, causing the filter membrane to be blocked, affecting the continuity of production. For this reason, the filtration device in step S6 is preferably a cross-flow filtration device, such as the attached Figure 3 As shown, the cross-flow filtration device includes a shell 1, an outer core 3 and an inner core 2 are arranged inside the shell 1, and the outer core 3 and the inner core 2 are both cylindrical filtration structures with closed bottoms, and conventional tubular filtration membranes or other tubular filtration materials can be used; the inner core 2 is arranged inside the outer core 3, and the inner core 2 and the outer core 3 are arranged coaxially, and the inner core 2 has a first filter chamber 6 inside, a salt water chamber 5 is formed between the inner core 2 and the outer core 3, and a second filter chamber 7 is formed between the shell 1 and the outer core 3, and the inner core 2 and the outer core 3 can at least rotate in the opposite direction to each other. The opposite rotation includes at least one of the following states: when the inner core 2 rotates forward, the outer core 3 rotates backward accordingly, when the inner core 2 rotates backward, the outer core 3 rotates forward accordingly, and when the inner core 2 rotates forward and reverse alternately, the outer core 3 rotates reversely and forward alternately.

[0055] Thus, the mixed liquid in the buffer tank is injected into the salt water chamber 5. As the inner core 2 and the outer core 3 rotate, part of the salt water enters the first filter chamber 6 after being filtered by the inner core 2, and part of the salt water enters the second filter chamber 7 after being filtered by the outer core 3. The filter residue intercepted by the inner core 2 and the outer core 3 will be continuously washed by the salt water in the salt water chamber 5 as the inner core 2 and the outer core 3 rotate, and will be separated from the inner core 2 and the outer core 3, forming an internal and external bidirectional cross-flow filtration, which not only increases the filtration area, but also prevents the filter residue from adhering to the surface of the filter core, preventing the clogging of the filter core, maintaining the continuous operation of the filtration, and improving the filtration efficiency. At the same time, due to the mutual reverse rotation between the inner core 2 and the outer core 3, the turbulence of the water flow in the salt water chamber 5 is aggravated, the force of the salt water washing the surface of the filter core is increased, and the water flow dead zone in the salt water chamber 5 is avoided, which can further improve the filtration efficiency.

[0056] For the rotation of the inner core 2 and the outer core 3, the cross-flow filtration device includes a driving device 4, a central axis 21 is arranged at the bottom of the inner core 2, an outer shaft sleeve 31 is arranged at the bottom of the outer core 3, the outer shaft sleeve 31 is sleeved on the outside of the central axis 21 and is coaxially arranged with the central axis 21, the central axis 21 and the outer shaft sleeve 31 can rotate relative to each other, and the central axis 21 and the outer shaft sleeve 31 are respectively connected to the driving device 4, so that the inner core 2 and the outer core 3 can at least rotate in opposite directions to each other.

[0057] When the center shaft 21 and the outer sleeve 31 are set, a water seal is set between the center shaft 21 and the bottom of the outer core 3 or the outer sleeve 31, and a water seal is set between the outer sleeve 31 and the bottom of the shell 1. Therefore, on the basis of setting the center shaft 21 and the outer sleeve 31 and ensuring their rotation, corresponding water seals are set to perform sealing treatment to prevent brine from leaking directly from the bottom of the outer core 3 into the shell 1, and to prevent brine from leaking directly from the bottom of the shell 1 into the external environment.

[0058] Regarding the specific content of driving the inner core 2 and the outer core 3 to rotate in opposite directions, two driving implementation forms are proposed in this application:

[0059] 1. The driving device 4 includes two independent motors, which are respectively denoted as the first motor and the second motor. The central shaft 21 is directly connected to the first motor, and the outer sleeve 31 is driven by the second motor through a pulley; thus, by adjusting the rotation direction of the two motors, various rotation forms such as reverse rotation and same-direction rotation between the inner core 2 and the outer core 3 can be achieved.

[0060] 2. The drive device 4 is provided with only one motor, as shown in the attached Figure 4 , 5 As shown, specifically, the driving device 4 includes a motor and a gear box. A gear assembly is arranged inside the housing 85 of the gear box. The gear assembly includes a central gear 81, a planetary gear 82, a driven gear ring 83, and a planet carrier 84. The driven gear ring 83 surrounds the outside of the central gear 81 and the planetary gear 82. The planetary gear 82 is located between the central gear 81 and the driven gear ring 83. The planetary gear 82 meshes with the central gear 81 and meshes with the inner teeth of the driven gear ring 83. The planetary gear 82 is fixedly connected to the housing 85 through the planet carrier 84. One side of the central gear 81 is connected to the central shaft 21, and the other side is connected to the motor. The outer sleeve 31 is connected to the driven gear ring 83. For the motor, it includes a rotor 91 and a stator 92. The central gear 81 is connected to the rotor 91.

[0061] Thus, by setting up a gear box and a motor, through the rotation of the motor (either forward or reverse), while the motor drives the center gear 81 and the center shaft 21 to rotate, the planetary gear 82 rotates in the opposite direction relative to the center gear 81. Since the planetary carrier 84 is fixed, the planetary gear 82 only transmits and drives the driven ring gear 83 to rotate in the opposite direction relative to the center gear 81. The outer sleeve 31 rotates with the driven ring gear 83, so that the center shaft 21 and the outer sleeve 31 can generate relative rotation in the opposite direction, and accordingly, the inner core 2 and the outer core 3 can rotate in the opposite direction.

[0062] For the injection or discharge of the mixed liquid in the buffer tank and the discharge of the filtrate after filtration, corresponding material pipelines can be set in the cavities corresponding to the first filter chamber 6, the brine chamber 5, and the second filter chamber 7 to provide for the flow of materials, for example, a liquid injection pipeline and a liquid extraction pipeline are set in the brine chamber 5, a liquid extraction pipe 61 is set in the first filter chamber 6, and a liquid outlet 71 connected to the second filter chamber 7 is set in the housing 1. In addition, the liquid extraction pipe 61 may not be set, and the central axis 21 may be changed to a hollow axis with a cavity, and the cavity is connected to the first filter chamber 6, so that the filtrate in the first filter chamber 6 can flow along the cavity to the outside of the cross-flow filtration device, thereby realizing the gravity self-drainage of the first filter chamber 6.

[0063] During the acidification process of step S5, most of the aluminum reacts to form aluminum hydroxide, but there are still trace aluminum elements remaining in the salt water in the form of aluminum ions after acidification. The remaining trace aluminum ions cannot be removed by filtering in step S6 alone, which easily leads to a high aluminum content in the final salt water. For this reason, the present application further improves step S6. Specifically, step S6 includes:

[0064] S61, sending the salt water in the buffer tank to a filtering device for filtration, and sending the filtered clear liquid to a treatment tank;

[0065] S62, adding a magnetized modifying agent to the treatment tank, stirring, and then adding sodium hydroxide to adjust the pH value of the brine to 7.0-7.6;

[0066] S63, sending the mixed liquid in the treatment tank to the magnetic sedimentation tank, using magnetic force to adsorb the magnetized modified treatment agent, and sending the supernatant to the brine tank.

[0067] The magnetized modification agent is a magnetic chitosan microsphere with sodium polyacrylate grafted on the surface. The volume of the clear liquid after filtration by the filter device is taken as the benchmark, and the magnetized modification agent with a particle size of 400-800 microns is taken. The usage amount of the magnetized modification agent is 30-100 particles / L. Thus, in the treatment tank, by adding the magnetic chitosan microsphere with sodium polyacrylate grafted on the surface into the salt water, the calcium, magnesium and aluminum ions remaining in the salt water are adsorbed, and as the salt water becomes weakly alkaline, they can be more stably attached to the surface of the microspheres, thereby realizing the secondary removal of aluminum in the salt water, and can effectively reduce the aluminum content in the salt water. Correspondingly, the calcium and magnesium ions that may remain in the salt water can also be further removed.

[0068] For the magnetic sedimentation tank, an electromagnetic generating device, such as an electromagnet, is arranged at the bottom of the magnetic sedimentation tank to generate magnetic force under the action of electricity, and magnetically adsorb the magnetized modified treatment agent entering the magnetic sedimentation tank, so that the magnetized modified treatment agent carries the calcium, magnesium and aluminum elements attached to its surface for rapid sedimentation, which is beneficial to improve the separation efficiency of the supernatant and also improves the production efficiency.

[0069] For the magnetized modifying agent, the preparation process is as follows:

[0070] B1, taking an acetic acid solution with a volume fraction of 2%-4%, dissolving chitosan powder in the acetic acid solution to obtain a chitosan solution with a mass fraction of 2.5%-3.0%;

[0071] B2, adding nickel powder with a particle size of 100-200 microns to the chitosan solution, stirring evenly, dripping the chitosan solution into a curing bath to solidify into balls, and filtering to obtain magnetic chitosan microspheres;

[0072] The mass ratio of nickel powder to chitosan is 0.01-0.05. The curing bath is an ethanol solution containing sodium hydroxide, the volume fraction of ethanol is 10%-40%, and the mass fraction of sodium hydroxide is 5%-15%;

[0073] B3, take a 4% sodium bisulfite solution, heat it to 55-65°C, add magnetic chitosan microspheres under stirring, and then drop acrylic acid monomer and ammonium persulfate solution into the sodium bisulfite solution at the same time;

[0074] The mass ratio of acrylic acid monomer to magnetic chitosan microspheres is 0.3-0.6, and the mass ratio of ammonium persulfate to acrylic acid monomer is 1:200-400.

[0075] B4. After the addition is completed, the reaction is kept warm for 2-4 hours, and then sodium hydroxide solution is added to adjust the pH to 7.2-7.6. After filtering, magnetic chitosan microspheres with sodium polyacrylate grafted on the surface are obtained.

[0076] Therefore, the present application utilizes magnetic chitosan microspheres as a matrix and grafts them with sodium polyacrylate. On the one hand, since both chitosan and sodium polyacrylate have good heavy metal ion treatment capabilities, the removal effect of calcium, magnesium and aluminum ions can be improved, and the burden of treating calcium / magnesium ions and aluminum elements in subsequent processes can be reduced. On the other hand, the adsorbed calcium, magnesium and aluminum ions can be relatively stably attached to the surface of the microspheres, and then in the magnetic sedimentation tank, as the magnetized modified treatment agent quickly settles under the action of magnetic force, the separation efficiency of the supernatant and the solid matter is greatly improved.

[0077] Example 1

[0078] A1. Salting. Mix water and solid raw salt to obtain saturated crude brine;

[0079] A2, primary reaction. Saturated crude brine, excess sodium carbonate, and excess sodium hydroxide are fed into the primary reaction tank to fully react to generate calcium carbonate and magnesium hydroxide; based on the unit volume of saturated crude brine, the amount of sodium carbonate is 400 mg / L, and the amount of sodium hydroxide is 200 mg / L; the temperature of the primary reaction tank is 60°C;

[0080] A3. Secondary reaction. The sodium hydrogen phosphate and the mixed solution in the primary reaction tank are sent to the secondary reaction tank, so that the remaining calcium and magnesium ions react fully to form calcium hydrogen phosphate and magnesium hydrogen phosphate; the amount of sodium hydrogen phosphate added exceeds the theoretical amount required for the reaction by 10ppm; the temperature of the secondary reaction tank is room temperature;

[0081] A4. Send the mixed liquid in the secondary reaction tank to the Kai membrane filter for filtration;

[0082] A5. Add hydrochloric acid to the filtered brine and send it to a buffer tank, so that the pH of the brine in the buffer tank is 5-6, and the aluminum element reacts to form aluminum hydroxide colloid;

[0083] A6. Send the salt water in the buffer tank to the filtering device for filtration, and send the filtered clear liquid to the treatment tank;

[0084] A7, add a magnetized modifying agent to the treatment tank, stir, and then add sodium hydroxide to make the pH value of the brine at 7.0-7.6; the magnetized modifying agent is a magnetic chitosan microsphere with a surface grafted sodium polyacrylate, and the magnetized modifying agent with a particle size of 400-800 microns can be used, and the amount used is 60 particles per liter of brine;

[0085] A8. Send the mixed liquid in the treatment tank to the magnetic sedimentation tank, use magnetic force to adsorb the magnetized modified treatment agent, and send the supernatant to the brine tank.

[0086] The brine in the brine tank was tested for calcium and magnesium ion content (calculated as calcium) and aluminum element content. The results are shown in Table 1.

[0087] Example 2

[0088] This embodiment omits the operations of steps A7-A8 of embodiment 1, and the operations of the remaining steps are completely consistent with the embodiment, and the clear liquid filtered in step A6 is sent to the brine tank. The brine in the brine tank is tested for the content of calcium and magnesium ions (calculated as calcium) and the content of aluminum element, and the results are shown in Table 1.

[0089] It should be noted that the specific steps in Example 1 and Example 2 are consistent with the relevant contents in the specific implementation mode of this application. In order to avoid redundancy, this application briefly describes the relevant contents in Example 1 and Example 2.

[0090] Table 1 Calcium and magnesium ion (calculated as calcium) content, aluminum element content test results

[0091]

[0092] It can be seen from Table 1 that the brine treatment method proposed in this application can effectively reduce the content of calcium and magnesium ions and the content of aluminum; for the content of calcium and magnesium ions, this application can reduce it to a level close to the Ca content of the electrolytic cell brine. 2+ / Mg 2+ Control index, in the subsequent process of secondary removal of calcium and magnesium ions by the chelating resin tower, the adsorption load of the chelating resin tower can be greatly reduced. As for the aluminum content, the present application can effectively precipitate and remove the aluminum element, so that the aluminum content in the treated brine can reach the aluminum control index of the electrolytic cell brine.

[0093] In addition, by comparing Example 1 with Example 2, it can be seen that: after removing calcium, magnesium ions and aluminum elements, the present application uses a magnetized modification agent to perform secondary treatment on the brine to adsorb the calcium, magnesium and aluminum ions remaining in the brine, which not only achieves secondary removal of aluminum elements in the brine, further reducing the aluminum content in the brine, but also can further remove the remaining calcium and magnesium ions in the brine.

[0094] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principle of the present invention should be included in the protection scope of the present invention.

Claims

1. A method for removing aluminum from brine used in a chlor-alkali electrolysis process, characterized in that: The method comprises: S1, mixing water and solid raw salt to obtain saturated crude brine; S2, sending saturated crude brine, sodium carbonate and sodium hydroxide into a primary reaction tank to fully react to generate calcium carbonate and magnesium hydroxide; S3, sending the mixed solution of disodium hydrogen phosphate and the primary reaction tank into the secondary reaction tank, so that the remaining calcium and magnesium ions fully react to form calcium hydrogen phosphate and magnesium hydrogen phosphate; S4, sending the mixed liquid in the secondary reaction tank into a filter for filtering; S5, adding hydrochloric acid to the filtered brine and sending it to a buffer tank, so that the pH of the brine in the buffer tank is 5-6, and the aluminum element reacts to form aluminum hydroxide colloid; S6, sending the mixed liquid in the buffer tank to a filtering device for filtration, and sending the filtered clear liquid to a brine tank; The temperature of the mixed liquid in the primary reaction tank is not less than 55°C; a plurality of steam heating pipes are evenly arranged in the primary reaction tank, and the steam heating pipes have a steam outlet for directly conveying steam into the primary reaction tank; the temperature of the mixed liquid in the secondary reaction tank is 10-20°C; Step S6 includes: S61, sending the salt water in the buffer tank to a filtering device for filtration, and sending the filtered clear liquid to a treatment tank; S62, adding a magnetized modifying agent to the treatment tank, stirring, and then adding sodium hydroxide to adjust the pH value of the brine to 7.0-7.6; S63, sending the mixed liquid in the treatment tank to a magnetic sedimentation tank, using magnetic force to adsorb the magnetized modified treatment agent, and sending the supernatant to a brine tank; Wherein, the magnetized modification agent is magnetic chitosan microspheres with sodium polyacrylate grafted on the surface; and an electromagnetic generating device is arranged at the bottom of the magnetic sedimentation tank.

2. A method for removing aluminum from brine used in a chlor-alkali electrolysis process according to claim 1, characterized in that: The water in step S1 at least includes dechlorinated salt water containing hypochlorite ions returned from the downstream ion membrane electrolysis process.

3. A method for removing aluminum from brine used in a chlor-alkali electrolysis process according to claim 2, characterized in that: The hypochlorite ion concentration in the dechlorinated brine is 5-40 mg / L, and the chlorate ion concentration in the mixed solution at the outlet of the secondary reaction tank is lower than 1-3 mg / L, so that the organic matter content in the mixed solution at the outlet of the secondary reaction tank is ≤10 ppm.

4. The method for removing aluminum from brine used in chlor-alkali electrolysis process according to claim 1, characterized in that: In step S2, based on the unit volume of saturated crude brine, the amount of sodium carbonate over-alkali is 300-500 mg / L, and the amount of sodium hydroxide over-alkali is 100-300 mg / L.

5. The method for removing aluminum from brine used in chlor-alkali electrolysis process according to claim 1, characterized in that: In step S3, based on the residual calcium and magnesium ion contents in the mixed solution fed into the secondary reaction tank, the amount of disodium hydrogen phosphate added exceeds the theoretical amount required for the reaction by 10-20 ppm.

6. The method for removing aluminum from brine used in chlor-alkali electrolysis process according to claim 1, characterized in that: In step S5, the buffer tank comprises a tank body (101), the tank body (101) has a liquid discharge port (109) and a liquid inlet, the brine pipe (102) is connected to the liquid inlet of the tank body (101), and along the direction of brine flow, a venturi acidifier (103) and a pH meter (104) are sequentially arranged in the brine pipe (102), the venturi acidifier (103) has an acid addition port, and the acid addition port is connected to a hydrochloric acid main line (105), a main regulating valve is arranged in the hydrochloric acid main line (105), the hydrochloric acid main line (105) has a branch pipe (106) connected in parallel with the main regulating valve, and a fine adjustment valve is arranged in the branch pipe (106).

7. A method for removing aluminum from brine used in chlor-alkali electrolysis process according to claim 6, characterized in that: A compressed air pipe (107) and a gas distributor (108) are arranged in the tank body (101); one end of the compressed air pipe (107) is connected to an external air source, and the other end is connected to the gas distributor (108); the gas distributor (108) has a plurality of evenly distributed air outlet holes.

8. The method for removing aluminum from brine used in chlor-alkali electrolysis process according to claim 1, characterized in that: In step S6, the filtering device is a cross-flow filtering device.

9. A method for removing aluminum from brine used in chlor-alkali electrolysis process according to claim 8, characterized in that: The cross-flow filtration device comprises a shell (1), an outer core (3) and an inner core (2) are arranged inside the shell (1), the inner core (2) is arranged inside the outer core (3), and the inner core (2) and the outer core (3) are arranged coaxially, a first filter cavity (6) is provided inside the inner core (2), a salt water cavity (5) is formed between the inner core (2) and the outer core (3), a second filter cavity (7) is formed between the shell (1) and the outer core (3), and the inner core (2) and the outer core (3) are at least capable of rotating in opposite directions relative to each other.

10. A method for removing aluminum from brine used in chlor-alkali electrolysis process according to claim 9, characterized in that: The cross-flow filtering device comprises a driving device (4); a central axis (21) is arranged at the bottom of the inner core (2); an outer shaft sleeve (31) is arranged at the bottom of the outer core (3); the outer shaft sleeve (31) is sleeved outside the central axis (21) and is arranged coaxially with the central axis (21); the central axis (21) and the outer shaft sleeve (31) are capable of relative rotation; the central axis (21) and the outer shaft sleeve (31) are respectively connected to the driving device (4) so ​​that the inner core (2) and the outer core (3) are at least capable of relative rotation.

Images